(1) Field of the Invention
This invention relates to a control device for a battery, which is charged by an electric power supplied through a power supplying line for charging the battery.
(2) Description of the Related Art
A battery loaded on a hybrid or electric vehicle for supplying power to a motor for traveling is charged as the need arises by reverse electromotive force arising in the motor upon speed reducing of the vehicle or an electric power from an alternator drived by an engine.
It is well known that a full charging capacity of a battery changes depending on change in surrounding temperature. If the change in the full charging capacity is not followed correctly, a charge of battery is controlled on the basis of a constant full charging capacity in spite of temperature change, resulting in an overcharging of the battery and deterioration in a charging performance of the battery.
A measure to solve the above problem may be as follows: a charging current flowing in a power supplying line for charging the battery and a terminal voltage of the battery are measured; a correlation between the charging current and the terminal voltage is computed; and a full charging capacity of the battery is evaluated on the basis of the correlation.
A change in an internal impedance of the battery when the battery approachs its fully charged state varies depending upon surrounding temperature. Therefore, when the battery is controlled on the basis of the full charging capacity simply derived from the correlation between the charging current and the terminal voltage without taking a factor of temperature into consideration, the battery might not be controlled properly since the full charging capacity derived in such a manner is not accurate.
The problem in controlling a battery described above widely arises for general batteries subjected to repeated charge and discharge besides the battery loaded on a hybrid or electric vehicle.